1Biomedical Research Laboratory, Ahfad University for Women, Omdurman, Sudan
2Department of Medical Parasitology and Mycology, School of Public Health, University of Medical Sciences, Tehran, Iran
3Professor emeritus of Microbiology, Ahfad University for Women, Omdurman, Sudan
Background: A β-mercaptoethnol (β-ME)-treated promastigote antigen of L. donovani was successfully employed in direct agglutination test (DAT) for the diagnosis of visceral leishmaniasis (VL). Objective: The β-ME-treated antigen was further incorporated into an enzyme-linked immunosorbent assay set-up (β-ME ELISA) and evaluated for VL diagnosis against outcome of reference freeze-dried DAT (FD-DAT) and rK39 strip test (RKT) commercial kits. Methods: Two-hundred and ninety-two sera from patients with high VL suspicion of whom 105 had confirmed L. donovani infection were tested. Results: Relatively higher sensitivities of 93.3% (95% CI: 88.4- 98.2) and 92.4% (95% CI: 87.3-97.5) were determined for β-ME ELISA and FD-DAT as compared to 83.8% (95% CI: 76.7-90.8) for RKT. Of 73 VL sera that scored maximum absorbance values (>0.81) in β-ME ELISA, 66 (90.4%) tested at the highest agglutination titres (>1:51200) in FD-DAT as did 56 (76.7%) also at comparable reaction intensities (3 + colour intensity) in RKT. Compared with FD-DAT (94.7%, 95% CI: 91.5-97.9) or RKT (93.0%, 95% CI: 89.3-96.6), lower specificity was estimated for β-ME ELISA (90.4%, 95% CI: 86.1-94.6). Based both on positive and negative microscopy for L. donovani in organ aspirates of all VL suspects enrolled (292), significantly higher correlation (p<0.01, 0.919) was established between β-ME ELISA and FD-DAT than between β-ME ELISA and RKT (p<0.01, 0.824). Taking into calculation the combined estimates of sensitivity, specificity, positive and negative predictive values, higher agreement (94.8%) was determined between total performance of β-ME ELISA and FD-DAT than between that of β-ME ELISA and RKT (90.7%). Conclusion: Based on results and merits discussed, we recommend application of this β-ME ELISA both for diagnosis of VL at laboratory level and confirmation of results obtained with DAT or RKT in the field.